The gamma-aminobutyric acid A receptor (GABAA) ion channel containing the α5 subunit is highly expressed in the hippocampus which is a key to cognitive function. Compounds with α5 subtype selective negative allosteric modulator (NAM) activity have been shown to improve cognition in rodent behavioral models (see non patent literatures 1-3). Similar phenotypes have been observed in animals with point mutations of the α5 subunit. These observations indicate that a GABAA α5 NAM is likely to treat cognitive disorders like Alzheimer's disease or to produce cognitive enhancement in human. Indeed, the α5 subtype selective NAM, α5IA has shown to block the alcohol-induced memory impairment of word list learning in healthy volunteers (see non patent literature 4).
Compounds that show NAM activity on all GABA receptor subtypes cause convulsions or have proconvulsant activity. Therefore, drugs which have affinity and selectivity for the GABAA α5 and act as GABAA α5 NAM are desired. However, because of the high homology among the primary sequences of GABA receptor subtypes, it has proven difficult to identify compounds that show high selectivity to one subtype over the other members in the family.
Meanwhile, it has been described in patent literature 1 that a compound represented by formula (A):

wherein WA is oxygen or sulfur; XA is optionally substituted lower alkyl, optionally substituted aryl or optionally substituted heteroaryl; YA is hydrogen or lower alkyl; ZA is optionally substituted lower alkyl; and TA is optionally substituted aryl or optionally substituted heteroaryl; selectively binds to GABAA receptors and is a highly selective agonist, antagonist or inverse agonist for GABAA brain receptors.
In addition, Patent literature 1 describes the following intermediate compound:
